Getting error in making signed apk when i use this library

I have developed one project and used this library but when i make signed apk then it is showing error like:

Error:(42, 57) error: package com.github.ksoichiro.android.observablescrollview does not exist Error:(43, 57) error: package com.github.ksoichiro.android.observablescrollview does not exist Error:(44, 57) error: package com.github.ksoichiro.android.observablescrollview does not exist Error:(45, 57) error: package com.github.ksoichiro.android.observablescrollview does not exist Error:(56, 85) error: cannot find symbol class ObservableScrollViewCallbacks Error:(70, 5) error: cannot find symbol class ObservableGridView Error:(310, 41) error: cannot find symbol class ScrollState

App is working fine if i run it in device via ADB. It shows this error when i try to generate signed apk

please provide me solution